Internal Carotid Artery Dissection Presenting with Transient or Subclinical Horner Syndrome

The most frequently encountered symptoms in internal carotid artery dissection (ICAD) are head or neck pain and cerebral ischemia. Ocular symptoms or signs have been reported as the presenting feature in up to 50% of patients, with (painful) Horner syndrome being the most frequently associated. Horner syndrome is part of the classic triad that depicts the characteristic presentation of ICAD and that consists of pain in the ipsilateral neck, head and orbital regions, (partial) Horner syndrome, and cerebral or retinal ischemia. All patients presenting with painful Horner syndrome should therefore require prompt investigations to rule out carotid artery dissection. In patients with confirmed diagnosis, treatment should be started early to prevent permanent ocular or cerebral complications.

Case 1: A 61-year-old woman presented with right temporal headache, an episode of transient visual loss and drooping of the right upper eyelid. Examination revealed anisocoria, which was more important in darkness. Reversal of anisocoria was observed after instilling drops of apraclonidine 0.5%. Neuroimaging demonstrated intrapetrous ICAD. Headaches, eyelid ptosis, and anisocoria all had resolved the next day. Apraclonidine pharmacologic testing a few weeks later was no longer dilating the previously smaller pupil. Case 2: A 48-year-old man presented with drooping of the right upper eyelid and right occipital headache and facial pain that all started one day after an intense yoga workout. Anisocoria was noticed upon examination, with topical cocaine 10% pharmacologic testing confirming a right Horner syndrome. Neuroimaging revealed ICAD. The patient reported resolution of his eyelid ptosis a few days later. Eyelid ptosis and anisocoria had indeed resolved at a follow-up examination a few weeks later. However, cocaine drop testing still produced anisocoria, compatible with subclinical Horner syndrome.

Transient or subclinical Horner syndrome can be the presenting feature in ICAD; in such cases, the characteristic eyelid ptosis and anisocoria may be short-lived and resolve in only a few days. If suspected by clinical history, pharmacologic testing may be helpful in identifying subclinical cases.